Williams plans 'substantial changes' for 2018 Formula 1 season

Williams is currently fifth in the constructors' championship with 45 points but is locked in a tight midfield battle with Toro Rosso, Haas and Renault, with just 11 points separating the four teams.

"We will be making some quite substantial changes," said Lowe, who joined the team from Mercedes ahead of this season.

"There are lots of different things that we'll be doing and we're well into that at the moment.

"There will be quite a few areas where we will be changing philosophy."

Felipe Massa said Williams is falling behind in the development race, after both its cars failed to progress from Q1 in qualifying for the Belgian Grand Prix

When asked by Autosport if he agreed with that standpoint, Lowe said: "That's always possible.

"It's difficult to conclude anything from single races, as there is a lot of variation from circuit to circuit.

"We have to look at the trends. We are fighting hard in that midfield group. We haven't created any distance ahead of it but if anything we've slipped well into it in the last couple of months.

"We need to understand if that's something where we're going wrong or if we have been out-developed."

Lowe said Williams, which is believed to have the sixth biggest budget of the 10 teams, was working hard to get the most out of its resources but conceded the team could be more efficient.

"We need to improve in all sorts of areas, that's the nature of the competition," he said.

"We have a set of resources and it's our job to do the best we can with those resources. It's about efficiency.

"We can be a lot more efficient than we are being at the moment.

"As we achieve more success, that will attract more resources to improve ourselves still further. That's the formula of grand prix development."